24 Surgical Positioning and Exposures

1.36

Interhemispheric Approaches

Interhemispheric approaches are used
to expose certain aneurysms of the anterior
communicating artery region. They are the
preferred approaches to most aneurysms of
the anterior cerebral artery distal to the an-
terior communicating artery and to arte-
riovenous malformations of the lateral
ventricle, third ventricle, basal ganglia, and
thalamus.

Interhemispheric Approach: Precallosal

1.36 The patient's head is
maintained at 0 degrees rotation.

1.37 The patient is placed in
the supine position with the thorax elevated
15 degrees; the head is extended to enhance
the surgeon's trajectory to the target.

1.37

Supine: Interhemispheric Approaches (Precallosal) 25

1.38 An 8-cm linear incision
is made in a skin crease of the forehead.
The surgeon positions the bone flap as low
as the frontal sinus will permit. The frontal
sinus is opened and obliterated (if neces-
sary) to achieve a low trajectory.

Two entry burr holes are made adja-
cent to the superior sagittal sinus. The edge
of the sagittal sinus is dissected from the
bone. The bone flap (4x4 cm) is cut with a
craniotome.

26 Surgical Positioning and Exposures

1.39

1.39 The dura is opened to
reflect over the sagittal sinus.

1.40 Preoperative evaluation
of the venous anatomy of the right hemi-
sphere allows the surgeon to select a corri-
dor along the midline that will obviate
sacrifice of critical bridging veins. The sur-
geon can gain additional exposure by dis-
secting the arachnoid overlying the vein
and by freeing the vein from the underlying
cortex and the dural flap.

Supine: Interhemispheric Approaches (Precallosal) 27

1.40

1.41

1.41 The self-retaining re-
tractor is attached to the skull-fixation de-
vice. A single retractor is placed on the
medial aspect of the frontal gyrus; a second
retractor is positioned to retract the falx
medially.

28 Surgical Positioning and Exposures

Closure 1.42 Following dural clo-
sure, the bone flap is secured with titanium
microplates and screws. All bone defects
are filled with methyl methacrylate to en-
hance the cosmetic result.

1.42

1.43 A thin sheet of Silastic
placed over the bony defect in the forehead
area prevents any shadow effect.

1.43

Supine: Interhemispheric Approaches (Callosal) 29

1.44

Interhemispheric Approach: Callosal

1.44 The patient's head is
maintained at 0 degrees rotation. A skin
flap is centered on the coronal suture,
crosses the midline, and is based laterally.

1.45 The patient is placed in
a supine position with the thorax elevated
15 degrees. The patient's head is flexed so
that the surgeon sites the target through the
bone flap.

1.45

30 Surgical Positioning and Exposures

1.46

Coronal suture

1.47

Sagittal
sinus

1.46 Two entry burr holes
are made adjacent to the superior sagittal
sinus. The edge of the sagittal sinus is dis-
sected from the bone. A bone flap (4x6
cm) centered on the coronal suture is cut
with a craniotome.

1.47 The surgeon drills holes
in the cranial edge and bone flap for placing
dural retention sutures and later placement
of stainless steel wires for bone flap fixa-
tion. The dural incision follows the margin
of the craniotomy.

Supine: Interhemispheric Approaches (Callosal) 31

1.48

1.49

1.48 The dural flap is hinged
on the edge of the sagittal sinus and re-
flected medially. A corridor is selected
between the bridging veins. Additional ex-
posure can be obtained by dissecting the
arachnoid overlying the vein; minor veins
are sacrificed. Preoperative evaluation of
the venous anatomy of the right hemisphere
will allow the surgeon to select a corridor
along the midline that will obviate sacrifice
of critical bridging veins. The surgeon can
obtain additional exposure by dissecting
the arachnoid overlying the vein and by
freeing the vein from the underlying cortex
and the dural flap.

1.49 Three self-retaining re-
tractors are inserted to pull the frontal lobe
laterally and the falx and sagittal sinus me-
dially. Adhesions between the cingulate
gyri are sectioned.

32 Surgical Positioning and Exposures

1.50

1.51

Closure 1.50 The dura is closed using
a continuous absorbable suture.

1.51 A dural retention suture
is placed through the center of the bone
flap, which is fixed with stainless steel
wires through the predrilled holes. The
ends of the wires are tucked into the drill
holes to prevent irritation of the overlying
skin. Any bone defects are filled with meth-
yl methacrylate to enhance the cosmetic
result.

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